The flavor profile of beer is subject to change during storage. Strecker aldehydes have been considered important constituents of aged flavor in beer. It has been proposed that Strecker aldehydes at least partly are formed from amino acids by transamination taking place between an amino acid and an α-dicarbonyl. In particular, it has been proposed that the amino acids listed in Table 1 may be involved in formation of Strecker aldehydes.
TABLE 1Taste pl of threshold Strecker amino of aldehydeamino acidacidStrecker aldehyde(ppb)Valine5.962-methyl propanal1000Isoleucine6.022-methyl butanal1500Leucine5.983-methyl butanal 600Methionine5.74Methional 250Phenyl alanine5.48Phenyl acetaldehyde1600
The flavour threshold for these aldehydes have been determined by Meilgaard, 1975, in Flavor chemistry in beer: Part II: Flavor and flavor threshold of 239 aroma volatiles, Tech. Q.—Master Brew. Assoc. Am., 12: 151-168 and are indicated in Table 1. Spiking beer with amino acids appears to result in increased levels of Strecker aldehydes. Thus Vesely et al., 2003 (Proceedings of the 29th European Brewery Convention Congress—(2003), 94/1-94/11) found increased levels of various Strecker aldehydes after spiking beer with amino acids.
However, the contribution of amino acids under normal conditions to the formation of aged flavor in beer has been disputed. Thus, one study found that 85% of the Strecker aldehydes present in aged beer are derived from Strecker degradation during wort production, while only 15% were derived from Strecker degradation in the bottled beer (Suda et al., Proceedings of the 31st European Brewery Convention Congress (2007), suda1/1-suda1/7). Thus the amino acid level in fresh beer appears to have little impact on the formation of Strecker aldehydes during beer aging.
Also it has been found that aldehydes formed during beer production are bound to other compounds, and said bound aldehydes may be released over time during storage (Baert et al., 2012, J. Agric. Food Chem., 60: 11449-11472). Thus attempts to reduce Strecker aldehydes in beer have been aimed at reducing formation and/or content of the aldehydes during production of beer. Baert et al., 2012 (vide supra) thus describes numerous practical measures to reduce aldehyde staling in beer including for example use of a yeast strain with high aldehyde reducing activity.